The invention relates to improved master brake cylinders for vehicles, such as automobiles, vans, and trucks.
The hydraulic brake system of vehicles, such as automobiles, vans, and trucks (hereinafter and in the claims referred to collectively as, xe2x80x9cvehiclesxe2x80x9d) consists of a master brake cylinder and pistons. The system is interconnected by pipes and hoses to disk brake calipers or wheel cylinders, located on each wheel of the vehicle. The master brake cylinder and its associated parts are filled with special high temperature resistant brake fluid. When the brake pedal is applied, its force is transmitted to the pistons of the master brake cylinder, which develops hydraulic pressure, which is then transmitted to the disk brake calipers or wheel cylinders.
To more fully understand the operation and design of a master brake cylinder, a typical master brake cylinder configuration is detailed in FIG. 1. In FIG. 1, there is illustrated a master brake cylinder 10. It is composed of a brake fluid reservoir 12, having primary port 14, and secondary port 16, as well as primary piston compensating port 18, and secondary compensating port 20, with all of these ports being in fluid communication with the interior of master brake cylinder 22.
Master brake cylinder 22 has positioned within its interior primary piston 24, having a front end 26, and a back end 28. Fitted to the front end 26 is primary seal 30. This seal is engaged by and partially held in position by its being urged against the concave side of spring retainer 32, which is attached to the piston by extension screw 36, described below. Spring retainer 32 has its non-concave side in contact with piston spring 34, which assists in holding the spring retainer 32 in place. Emanating from front end 26 of primary piston 24 is piston extension screw 36, which is attached to primary piston stop 38. The back end 28 of primary piston 24 is fitted with O-ring seal 40.
The back end 42 of secondary piston 44 is fitted with a secondary seal 46. The front end 48 of secondary piston 44 is fitted with primary seal 50, which is urged against the front end 48 by spring retainer 52. The front of spring retainer 52 engages one end of secondary piston spring 54, with the other end of secondary piston spring 54 being positioned along the end of master brake cylinder 22.
Two lines (not shown) deliver fluid from the master brake cylinder 22. The action of the brake is actuated by the driver of the vehicle depressing brake pedal (not shown), which is connected to output rod 60, which engages the back end 28 of primary piston 24.
When the brake pedal is depressed, it causes output rod 60 to move primary piston 24 and secondary piston 44 forward, compressing piston springs 34 and 54. As the pistons move forward, brake fluid is displaced into rear and front brake lines (not shown), which causes the front and rear brakes to engage the drums or calipers (not shown). Upon retraction of the output rod 60, brake fluid returns into the master brake cylinder 22, and primary piston spring 34 and secondary piston spring 54 urge the primary and secondary pistons 24 and 44 back to the status of the brake pedal not being applied. Primary and secondary piston compensating ports 18 and 20 prevent a vacuum from forming as the brake fluid returns. The seals on the primary and secondary pistons 24 and 44 prevent fluid from leaking beyond the pistons 24 and 44.
Seals for the pistons of master brake cylinders, particularly primary seals, have typically been retained on the pistons by mechanical spring retainers. These seal retainers increase the tolerance of the piston assembly stack and, therefore, the tolerance of the entire master brake cylinder assembly. A reduction in tolerance directly contributes to the improved travel to close performance of the master brake cylinder assembly. Travel to close is a vehicle performance parameter for pedal travel and pedal feel. Any elimination of parts also results in cost savings for the master brake cylinder assembly.
When seals are assembled over a piston and retained in a groove of the piston, only certain materials could be used. These materials had to be capable of being stretched for assembly and still retain enough elasticity to return to their original configuration once in the groove to seal against the piston. The assembly process for attaching the seals to the pistons requires the strenuous handling of the pistons. Because of this, the use of high temperature plastics as a material for producing pistons has not been fully exploited by the art. For instance, phenolic resins that are characteristically brittle would be damaged if dropped during the master brake cylinder assembly process, and, typically, seals become cut when assembled over the phenolic surface.
It would be beneficial to solve the above-described problems relating to the seals and at the same time reduce the cost of production and reduce the number of parts necessary in the master brake cylinder.
One aspect of the invention provides an improved master brake cylinder used in the braking systems of vehicles. These master brake cylinders comprise a cylinder, having a reservoir for supplying brake fluid to the cylinder. Within the cylinder, there are a primary piston and a secondary piston. Brake fluid resistant elastomeric seals are mechanically retained onto the primary and secondary pistons. The improvement made to these master brake cylinders resides in having the elastomeric seals molded directly onto the primary and secondary pistons.
Another aspect of the invention is an improved piston for master brake cylinders of vehicles that comprise a piston, having a front and a back, and having channels about their circumferences. Directly molded into the channels is a brake fluid resistant, synthetic elastomer seal. It should be understood that the present invention contemplates the use of commonly used brake fluids.
Another aspect of the invention resides in that the channels described above are U-shaped.
Another aspect of the invention has the channel in the back end containing a circumferential rib.
Another aspect of the invention involves the use of the pistons being made of metal, preferably a non-ferrous metal.
Another aspect of the invention allows plastics to be used to fabricate the pistons, with a preferred plastic being a phenolic resin.
Another aspect of the invention resides in molding to the pistons elastomers, which are chemically resistant to brake fluids. One such group of elastomers is the ethylene propylene elastomers, which includes terpolymers of these copolymers.
Another aspect of the invention utilizes as the brake fluid resistant elastomers such elastomers as chloroprene neoprene elastomers, fluorosilicone elastomers, sulphonate polyethylene elastomers, and chlorinated polyethylene elastomers.
Another aspect of the invention utilizes with phosphate ester brake fluids metal pistons, particularly, non-ferrous metal pistons, as well as plastic pistons, such as phenolic resin pistons.
The invention provides the foregoing and other features, and the advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention and do not limit the scope of the invention, which is defined by the appended claims and equivalents thereof.